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Polyelectrolyte multilayers of just a few nanometers thickness were used for direct bonding of silicon, thermally oxidized silicon, and borosilicate wafers, respectively, and the bonded wafer pairs were characterized during and after annealing at temperatures up to 350 °C. Determination of surface energy as a measure of bond strength was performed in situ during annealing. The bond strengths show an interesting temperature dependence which can be utilized for temporary bonding of silicon wafers. Infrared transmission photographs as well as FTIR and XPS measurements suggest that the formation of hydrogen bubbles, generated by the reaction between water and silicon, contributes to the debonding at elevated temperatures.

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Atmospheric pressure plasma treatments were used to control free surface energy of different areas on silicon wafers before bonding. Surface energy measurements in situ during annealing for this different areas are presented for SF6 etching as well as acetylene, glycidyl methacrylate, tetramethylsilane and C4F8 and coatings. The bonding energy can be permanently reduced by appropriate coatings or surface roughness. The results revel important aspects for the choice of precursors and parameters to obtain high contrast between the treated and untreated areas.